Television transmitter



y 1941- K. SCHLESINGER I TELEVI SION TRANSMITTER Filed Aug. 31, 1937 Patented July 8, 1941 FICE TELEVISION TRANSMITTER Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York- Application August 31, 1937, Serial No. 161,775

In Germany September 5, 1936 3 Claims.

The present invention relates to television transmitters and particularly to such transmitters operating according to the interlaced line method and with an odd' number of lines per image.

The invention consists in a connection for transmitting the short line and the longer frame synchronising impulses. A transmitter of the above character sends the frame synchronising impulses alternately at one end and in the middle of the last line of each picture field. If the impulses are taken from separate generators (output tubes of the synchronising impulses amplifiers) it is necessary to conduct them for modulating the transmitter onto a common lead, i. e. to mix them. The simplest way would be to switch both impulses in parallel via resistances. There arise, however, some difliculties which are overcome by the connection according to the invention.

The invention will fully appear from the following description in which reference will be made to the accompanying drawing in which Fig. 1 is a time diagram of the synchronising impulses when mixed by simple addition,

Fig. 2 is a connection for mixing the impulses according to the invention,

Figs. 3a and 3b are time diagrams of impulses mixed according to the invention, whilst Fig. 4 is a modification of Fig. 2.

When the line impulses 5 (Fig. 1) and the frame impulses 6 are mixed, as said above, by simple addition the sum of both is represented by the curve 'I which is not suitable for the desired use.

According to the invention the impulses of both kinds produced by separate generators are mixed in a special tube so that the arising amplitude is not higher than that caused by the single impulses.

Fig. 2 shows a diagram of the connection. The frame change generator I passes its impulses to the lead 2. The line change generator 3 is connected to supply its output to the lead 4. The mixing tube 8 has two control electrodes or grids 9 and III. This tube 8 may further be provided with a screening grid I I and an intercepting grid I2. A normal four or five electrode valve may be used which by way of an anode resistance I3 is connected to a suitable source of anode voltage, such as battery I4.

The leads 2 and 4 are connected by way of resistances 9a and We to the control grids 9 and I0 which are, in turn, earthed or grounded via resistances 9b, I0b. There accordingly flows a constant feed current, the intensity of which may be adjusted by the screening grid battery I la. This current is completely interrupted by the negative synchronisation impulses arriving at one of the grids 9 and I0. In this way there result in the output lead 20 positive impulses equal to the voltage drop at the anode resistance I3, and independent of whether lead 2 or 4 or both at once are excited. There is then obtained a synchronisation impulse diagram according to Fig. 3.

In Fig. 3a the frame change occurs at one end of a line, while in Fig. 3b the change occurs in the middle of a line.

In order to ensure the frame pump to be perfectly undisturbed there may be provided a. preliminary blocking of the line impulses just before the arrival of a frame impulse. The desired phase advance is readily obtained by a resistancecapacity coupling. In Fig. 4, which is based on Fig. 2, a coupling of the above-described character is indicated by the resistance and capacity combination I9 and 20. If it is assumed that the duration of a frame change impulse is of the order of 10 seconds, the condenser may have 0.01 mi. capacity and the resistance 20 may be of the order of 10,000 ohms. The advanced impulse so obtained is then supplied to the grid or control electrode 9 by way of the resistance 2| and the line impulses are accordingly cut out a short time before the frame change impulse arrives. In this way a mutual interfering between line and frame change impulses is completely avoided.

If, instead of positive synchronisation impulses on the output, negative ones are desired, a reversing stage has to be provided. The simplest way is to use a tube I l coupled by way of a condenser I5 to the mixing tube 8. The control electrode or grid of tube I4 is earthed via resistances I1 and I6 and a bias battery I8, the latter having a voltage sufiicient to suppress the anode current in the position of rest. The time constant of capacity I5 and resistor I6 has to be dimensioned so as to transmit satisfactorily an oscillation of a period equal to 10 times the duration of a frame synchronising impulse. Resistance I'I causes the impulses tohave a rectangular form and a constant amplitude.

I claim:

1. In a television system, a synchronizing impulse mixing circuit comprising a frame synchronizing impulse generator, a line synchronizing impulse generator, a thermionic tube having at least a cathode, a first control electrode, a second control electrode and an anode, impedance coupling means directly connecting said frame synchronizing generator to said first control electrode, impedance coupling means directly connecting said line synchronizing impulse generator to said second control electrode, a first resistance connected between said first control electrode and said cathode, a second resistance connected between said second control electrode and said cathode, a serially connected resistor and source of potential connected between said anode and said cathode, and means to derive output energy from across said serially connected resistance.

2. In a television system, a synchronizing impulse mixing circuit comprising a frame synchronizing impulse generator, a line synchronizing impulse generator, a thermionic tube having at least a cathode, a first control electrode, a second control electrode and an anode, impedance coupling means directly connecting said frame synchronizing generator to said first control electrode, impedance coupling means directly connecting said line synchronizing impulse generator to said second control electrode, a first resistance connected between said first control electrode and said cathode, a second resistance connected between said second control electrode and said cathode, a first current limiting resistance inserted between said first resistance and said first control electrode, and a second current limiting resistance inserted between said second resistance and said second control electrode.

3. In a television system, a synchronizing impulse mixing circuit comprising a frame synchronizing impulse generator, a line synchronizing impulse generator, a thermionic tube having at least a cathode, a first control eldectrode, a second control electrode and an anode, impedance coupling means connecting said frame synchronizing generator to said first control electrode, impedance coupling means to connect said line synchronizing generator to said second control electrode, a series circuit comprising a capacity and resistance element having the capacity element connected intermediate the output of the frame synchronizing impulse generator and its associated impedance coupling means and the resistance connected to the cathode of the said thermionic tube, and a resistance element having one terminal connected intermediate the capacity and resistance of the said series circuit and the other terminal connected intermediate the line synchronizing impulse generator impedance coupling and the second control electrode of said thermionic tube, a first resistance connected between said first control electrode and said cathode, a second resistance connected between said second control electrode and said cathode, a serially connected resistor and source of potential connected between said anode and said cathode, and means to derive output energy from across said serially connected resistance.

KURT SCHLESINGER. 

